[Math] Calculating by hand a surface gradient factor.

[huwporter]

The "gradient factor" a diver is experiencing at any given point of a dive is just the maximum of the percentages of permissible supersaturation across all compartments at that point.

A "Surf GF" is then easy to calculate at any point in time by calculating the ratio of supersaturation to the maximum permissible supersaturation that the diver would experience if they immediately went to 1ATA, for all compartments, and taking the maximum.

(For a deco dive, SurfGF will be higher than GFHi, and probably higher than 100%, at the end of the bottom phase, hence the need tor deco stops on the way up to allow SurfGF to drop. Deco is 'complete' when SurfGF drops below GFHi.)

E.g. the GF the diver is experiencing in column "GF", and SurfGF in the final column on the right under "SGF":

(Don't forget in all of this that compartments, permissible supersaturation etc are all just theoretical concepts that happen to be useful, not actual real things)

 

[atdotde]

Everything you are looking for including the calculation of the surface GF is in the Subsurface source code, in particular in subsurface/deco.c at master · subsurface/subsurface and subsurface/profile.c at ecfbf2a9ba51905a6915ba526979130ac134b744 · subsurface/subsurface
In particular, it integrates the differential equation in subsurface/deco.c at ecfbf2a9ba51905a6915ba526979130ac134b744 · subsurface/subsurface
The diffusion constant is ln(2)/half_time with half_time you vary between the different tissues.